1. Field of the Invention
This invention relates to an apparatus capable of suitably setting an optical environment and further a temperature environment suited to effect measurement of the photoelectric conversion characteristics (particularly such as smear, blooming, dark current, spectral sensitivity, sensitivity irregularity and defect of picture element) of an element, for example, an image pickup element such as a charge coupled device (CCD) or other similar element.
2. Description of the Prior Art
In recent years, attention has been paid to solid image pickup elements which can perform functions such as photoelectric conversion, charge accumulation, transfer, detection and processing merely by utilizing the physical properties of a solid. This is because solid image pickup elements have advantages of compactness, light weight and low power consumption as compared with image pickup tubes and moreover, because solid image pickup elements can be manufactured at low cost by mass production and can be readily utilized in various fields by the user. In fact, however, the optical environment characteristic and temperature environment characteristic of the photoelectric conversion characteristics such as smear, blooming, dark current, spectral sensitivity, sensitivity irregularity and defect of picture element are not stable as compared with image pickup tubes.
Therefore, from the viewpoint of quality inspection, it is desirable to measure the photoelectric conversion characteristics of image pickup elements in a predetermined optical environment and further in a predetermined temperature environment, but heretofore it has not been practiced to quantitatively measure the characteristics of the image pickup elements. Nor has it been practiced to partly imaging-illuminate an image pickup element or uniformly illuminate the whole image pickup element and systemwisely measure each characteristic in the same environment.
Particularly, in measuring smear or blooming, a pin hole imaging illumination or a slit imaging illumination having a length 1/10 as great as the length of the picture plane size of the image pick-up element (i.e., a partial illumination) is applied to the image pick-up element. The partial illumination has a quantity of light of each wavelength about 200 times as great as the saturation light quantity of the image pick-up element. During the parital illumination, carriers are generated in the portion of the substrate other than the light-receiving portion or in the lower portion of the substrate, and the carriers diffuse into the transfer portion of the image pick-up element, to result in a direct electric current. The resulting DC component is measured. On the other hand, in the measurement of spectral sensitivity, for example, a uniform illumination is provided to the whole of the image pickup element to thereby detect the sensitivity for each wavelength.
It is desirable that the part illumination and the whole illumination be quantitatively effected selectively in the same environment, whereas this has heretofore not been practiced. Now, in the measurement of the dark current of the image pickup element, the dark current varies to two times for a temperature rise of about 8.degree. C. and therefore, temperature control is necessary. Further, movement of the image pickup element may cause a flow of weak current which in turn may cause heat generation and may thereby cause a temperature rise, and from this viewpoint as well, temperature control is necessary in the measurement of the image pickup element.
It is known to provide a plurality of filters in the illuminating system and rotate a turret to select a desired filter from among the plurality of filters in order to vary the wavelength or the quantity of the illuminating light. That is, as shown in FIG. 1 of the accompanying drawings, a filter turret 2 having a plurality of different filters 1 is secured coaxially with a ratchet wheel 4 and the operator manually rotates the turret while visually confirming the setting on a scale 3 provided on the side surface or the like of the turret 2, and selects a desired filter 1 and interposes it between a light source 6 and an element 7. In this case, positioning and fixing of the selected filter 1 is accomplished by causing the pawl of a spring 5 to be received in a notch of the ratchet wheel 4.
As another example of the prior art, there is a method as shown in FIG. 2 of the accompanying drawings wherein a filter turret 2 is driven by a stepping motor 11 through a connecting gear 10. In this case, positioning of each of filters 1 provided on the turret 2 is accomplished as by providing a projection 8 or the like on the turret 2 and setting the reference position of the motor 11 by a switch 9.
However, in the measurement of the characteristics of the element, the frequency of the selection and positioning of the desired filter is high and the example of the prior art shown in FIG. 1 is inefficient and uneconomical. Also, in the example of the prior art shown in FIG. 2, the positioning accuracy of the filters depends on the accuracy of the stepping motor and, when a positional deviation occurs, the necessary re-adjustment is cumbersome. Further, the stepping motor has a disadvantage that unless a voltage is always applied thereto, the motor cannot fix the positions of the filters. In addition, the number of filters which can be mounted on a turret is limited and this leads to the necessity of interchanging the turret, but it is difficult and cumbersome to adjust the stopped positions of the filters and the motor each time the turret is interchanged.